Dipropylene glycol is a compound that is used as a raw material for polyester resin or polyurethane resin, a raw material for acrylates, an operating oil, an antifreezing solution, a wetting agent for cellophane, a compatibilizing agent, a solvent for printing ink, a raw material for cosmetics, solvent for perfume, solvent for toiletries, and so on, whereas tripropylene glycol is a compound that is used as a raw material for polyester resin or polyurethane resin, a raw material for acrylates, a solvent for a water-soluble oil, a solvent for ink, and so on. Dipropylene glycol and tripropylene glycol are known to be produced as byproducts when producing propylene glycol.
It is known that dipropylene glycol produced industrially is commonly a mixture of 1,1′-oxybis-2-propanol, 2,2′-oxybis-1-propanol, and 2-(2-hydroxypropoxy)-1-propanol (see, for example, non-patent document 1).
Moreover, it is known that tripropylene glycol produced industrially is commonly a mixture of 1,1′-[(1-methyl-1,2-ethanediyl)bis(oxy)]bis-2-propanol, 2,2′-[(1-methyl-1,2-ethanediyl)bis(oxy)]bis-1-propanol, 2-[1-(2-hydroxypropoxy)-1,2-propoxy]-1-propanol, and 2-[2-(2-hydroxypropoxy)-propoxy]-1-propanol (see, for example, non-patent document 1).
The proportion of 1,1′-oxybis-2-propanol contained in commercially available dipropylene glycol is 0.10 to 0.70, and the proportion of 1,1′-[(1-methyl-1,2-ethanediyl)bis(oxy)]bis-2-propanol contained in commercially available tripropylene glycol is 0.10 to 0.70. Such commercially available dipropylene glycol and tripropylene glycol are known to be produced as byproducts when producing propylene glycol by making propylene oxide react with excessive water in the absence of a catalyst (see, for example, non-patent document 1).
On the other hand, patent document 1, for example, discloses a production method to obtain an alkylene glycol with high selectivity while generating almost no dialkylene glycol or trialkylene glycol by making an alkylene oxide react with water in the presence of carbon dioxide using a compound one or more element selected from the group consisting of titanium, zirconium, vanadium, niobium, tantalum, and chromium as a catalyst.